Change In Refractive Power Research Articles

Research progress on the development of myopia prediction models and their predictive performance

The incidence of myopia is continuously increasing worldwide, especially in China, where the prevention and control of myopia is of great significance. Accurate prediction of myopia and early intervention are of great importance for slowing down the development of myopia and reducing the social burden. This article reviews the research progress of myopia prediction models and their predictive performance in recent years. It includes models based on refractive power and ocular biological characteristics, such as those using parameters such as refractive power, axial length, and percentile curves for prediction; models combined with environmental factors, which explore the relationship between myopia in school-age children and the age of onset, parents' myopia, education, and various living environmental factors; models based on genetic factors, which predict by evaluating parents' myopia status and single nucleotide polymorphisms discovered in genome-wide association studies. In addition, the article also introduces the application of artificial intelligence in myopia prediction, such as machine learning and deep learning algorithms that can predict changes in axial length growth and refractive power. These research advances provide a reference for establishing more accurate myopia prediction models and help achieve precise and personalized myopia prevention and control.

The relationship between contact lens ultraviolet light transmittance and myopia progression: a large-scale retrospective cohort study.

The prevalence of myopia is increasing dramatically around the world, and many studies have suggested the possibility that ultraviolet (UV) light is effective to prevent the onset and progression of myopia. However, UV is a risk factor for diseases that cause refractive errors such as cataract and pterygium. In this study, we evaluated the relationship between UV exposure and myopia progression. The dataset consisted of a total of 337 396 eyes of patients in the 12-to-29-year age range, who were prescribed soft contact lenses (SCL) for refractive error at Okada Eye Clinic in Japan between 2002 and 2011. They were tracked over a five-year period and did not change the type of SCL. In this retrospective cohort study based on medical records, we divided patients into two groups, one prescribed SCL with UV protection (UV-SCL), and another prescribed SCL without UV protection (UV+SCL). Change in refractive power over five years was measured and results compared. It was -0.413 diopter (D) in the UV-SCL group and -0.462 D in the UV+SCL group. Thus, the progression of myopia was slower in the UV-SCL group. The results were also analyzed separately by gender and degree of myopia at the time of initial prescription, which all showed significant differences (P<0.001). Results suggest that UV exposure may advance myopia. Further research is needed to investigate the underlying mechanisms that could explain this.

Regional Summed Corneal Refractive Power Changes in Myopic Orthokeratology and Their Relationships With Axial Elongation.

To determine the relationship between regional summed corneal refractive power changes (CRPCs) in myopic orthokeratology and axial elongation. This retrospective study included 70 eyes of 70 patients aged 8 years to 13 years who underwent orthokeratology lens (OK lens) treatment, and all patients underwent regular follow-ups at 1 week, 1 month, 6 months, and 12 months at Zhongshan Ophthalmic Center between January 2019 and May 2021. Axial length (AL) was measured at baseline and 12 months by an IOLmaster 5.0. Refractive error power was measured using cycloplegia. Regional summed CRPCs were calculated by MATLAB software using difference tangential power maps at the sixth month acquired by corneal topography measurements (Medmont E300 Corneal Topographer; Medmont Pty, Victoria, Australia) and defined as changes in corneal refractive power at the sixth month from baseline. The regional summed CRPCs were then subdivided into 4-mm diameter circles, 4- to 5-mm diameter chords, and 5- to 6-mm diameter chords according to the distance from the central of the pupil and into negative, positive, and total according to the values. Pearson correlation, multiple linear regression analysis, and stepwise multiple linear regression analysis were performed to analyze the relationships among these parameters. Axial elongation had a negative relationship with positive regional summed corneal refractive power in the central 4-mm diameter circle and age (r=-0.282, P =0.018; r=-0.473, P <0.001, respectively) and a positive relationship with negative regional summed corneal refractive power in the 5- to 6-mm diameter chord (r=0.361, P =0.002). Stepwise multiple linear regression analysis identified age (standardized β =-0.434, P <0.001) and negative regional summed corneal refractive power in the 5- to 6-mm diameter chord (standardized β =0.305, P =0.004) as factors influencing AL elongation. Negative regional summed corneal refractive power in a 5- to 6-mm diameter chord after OK lens treatment may be an important index for evaluating the control effects of axial elongation.

The influence of back optic zone diameter on relative corneal refractive power changes following orthokeratology fitting

The influence of back optic zone diameter on relative corneal refractive power changes following orthokeratology fitting

Epithelial Remodeling and Epithelial Wavefront Aberrometry after Spherical vs. Cylindrical Myopic Small Incision Lenticule Extraction (SMILE).

Background/Objectives: To compare the epithelial thickness changes and the changes in epithelial wavefront aberrometry following spherical versus astigmatic myopic small incision lenticule extraction (SMILE). Methods: Eighty-six eyes of 86 patients who underwent SMILE were included in this retrospective study. A total of 43 eyes underwent myopic spherical correction (spherical group) and 43 eyes underwent myopic cylindrical correction (cylindrical group). The groups were matched according to the spherical equivalent of surgically corrected refraction. Subjective manifest refraction as well as high-resolution anterior segment optical coherence tomography (MS-39; CSO; Florence, Italy) were obtained preoperatively as well as 3 months postoperatively. The latter was utilized for computing epithelial wavefront aberrometry in addition to epithelial thickness mapping. Results: Epithelial thickness increased significantly in both groups after SMILE (p < 0.01). In the cylindrical group, epithelial thickening was more pronounced on the flat meridian compared to the steep meridian (p = 0.04). In both groups, epithelial wavefront aberrometry showed a significant postoperative increase in the epithelium's spherical refractive power, causing a myopization of -0.24 ± 0.42 diopters (D) in the spherical group (p < 0.01) and -0.41 ± 0.52 D in the cylindrical group (p < 0.0001). While no significant changes in epithelial cylindrical refractive power were observed in the spherical group, a significant increase was noted in the cylindrical group from -0.21 ± 0.24 D to -0.37 ± 0.31 D (p = 0.01). In both groups, epithelial higher-order aberrations increased significantly (p < 0.001). Conclusions: Postoperative epithelial remodeling after SMILE alters lower-order (sphere and cylinder) and higher-order aberrations of the corneal epithelial wavefront and might contribute to refractive undercorrection, especially in astigmatic corrections. Epithelial wavefront aberrometry can be used to quantify the refractive effect of epithelial remodeling processes after keratorefractive surgery.

Longitudinal Study on Myopia Progression Considering Axial Length and Refraction in Caucasian Students

Purpose: Students are a risk group for myopia progression because of their intensive levels of near work. This study aimed to evaluate the progression of myopia in Caucasian students over a period of two years. Material and Methods: In a prospective multivariate longitudinal design over a period of two years, data from both eyes of 84 subjects (mean age = 23.7 ± 3.7 years; mean spherical equivalent = −2.01 ± 2.52 D) were randomized for statistical analysis. Axial length, non-cycloplegic refraction and corneal refractive power were measured using the Myopia Master (Oculus Optikgeräte GmbH, Germany). Additionally, data on near phoria, accommodation, outdoor activity, daily time with near work, and refractive influences were collected. Results: The subjects showed a statistically significant increase in axial length from baseline mean 23.98 ± 1.19 mm by 0.067 ± 0.025 mm ( = 0.010). The objective spherical equivalent (baseline mean = −2.01 ± 2.52 D) showed no statistically significant shift towards myopia (p = 0.113). In the moderate myopic subgroup, 40.0 %, 50.0 %, and 10.0 % showed axial myopia and refractive myopia of the crystalline lens or cornea, respectively. The main reasons for myopia progression were an increase in axial length (51.3 %), a change in refractive power of the lens (41.0 %), and a change in refractive power of the cornea (7.7 %). Near phoria and progression of myopia were correlated (p = 0.033). All other parameters were within the normal range and did not show a correlation with the progression of myopia. Conclusion: The risk group of Caucasian students showed neither a clinically relevant increase in axial length of the eye nor a change in objective spherical equivalent towards myopia over a period of two years. Nevertheless, the change in the refractive power of the crystalline lens is supposed to be an important factor for myopia progression, in addition to the change in axial length.

In vivo assessment of human corneal epithelial cells in orthokeratology lens wearers: A pilot study.

Central corneal epithelial thinning associated with midperipheral epithelial thickening has been reported as the main factor contributing to the effectiveness of orthokeratology (ortho-k) in myopia control. Yet, the cellular mechanism governing the regional change in refractive power remains elusive. This study aimed to evaluate the correlation between the regional change in corneal epithelial thickness and cell density in ortho-k wearers. A new human prototype of a polarization-dependent optical coherence microscope was developed to enable noncontact and noninvasive in vivo imaging of corneal epithelial cells in ortho-k wearers with and without their ortho-k lens. The epithelial thickness and cell density were evaluated at the central and midperipheral corneal locations in four ortho-k wearers and four spectacle wearers serving as controls. Polarization-dependent optical coherence microscope achieved in vivo volumetric imaging of all epithelial cell types in ortho-k wearers with and without their lens over a field of view of 0.5 × 0.5 mm2 with an isotropic resolution of ~2.2 mm. The central epithelial thinning and midperipheral epithelial thickening were consistent across all ortho-k wearers. However, the inconsistency in their regional epithelial cell density highlighted a great variability in individual response to ortho-k treatment. There was no strong correlation between epithelial thickness and cell density, especially at the midperipheral cornea, in ortho-k participants. This study constitutes our first step toward uncovering the cellular mechanism underlying the effectiveness of ortho-k in myopia control. Future studies will focus on the longitudinal evaluation of epithelial cells before and during ortho-k treatment to identify factors governing individual response to ortho-k treatment and ultimately inform the dynamics of epithelial cells taking place during the ortho-k treatment.

FEA-Based Stress-Strain Barometers as Forecasters for Corneal Refractive Power Change in Orthokeratology.

To improve the effectivity of patient-specific finite element analysis (FEA) to predict refractive power change (RPC) in rigid Ortho-K contact lens fitting. Novel eyelid boundary detection is introduced to the FEA model to better model the effects of the lid on lens performance, and stress and strain outcomes are investigated to identify the most effective FEA components to use in modelling. The current study utilises fully anonymised records of 249 eyes, 132 right eyes, and 117 left eyes from subjects aged 14.1 ± 4.0 years on average (range 9 to 38 years), which were selected for secondary analysis processing. A set of custom-built MATLAB codes was built to automate the process from reading Medmont E300 height and distance files to processing and displaying FEA stress and strain outcomes. Measurements from before and after contact lens wear were handled to obtain the corneal surface change in shape and power. Tangential refractive power maps were constructed from which changes in refractive power pre- and post-Ortho-K wear were determined as the refractive power change (RPC). A total of 249 patient-specific FEA with innovative eyelid boundary detection and 3D construction analyses were automatically built and run for every anterior eye and lens combination while the lens was located in its clinically detected position. Maps of four stress components: contact pressure, Mises stress, pressure, and maximum principal stress were created in addition to maximum principal logarithmic strain maps. Stress and strain components were compared to the clinical RPC maps using the two-dimensional (2D) normalised cross-correlation and structural similarity (SSIM) index measure. On the one hand, the maximum principal logarithmic strain recorded the highest moderate 2D cross-correlation area of 8.6 ± 10.3%, and contact pressure recorded the lowest area of 6.6 ± 9%. Mises stress recorded the second highest moderate 2D cross-correlation area with 8.3 ± 10.4%. On the other hand, when the SSIM index was used to compare the areas that were most similar to the clinical RPC, maximum principal stress was the most similar, with an average strong similarity percentage area of 26.5 ± 3.3%, and contact pressure was the least strong similarity area of 10.3 ± 7.3%. Regarding the moderate similarity areas, all components were recorded at around 34.4% similarity area except the contact pressure, which was down to 32.7 ± 5.8%. FEA is an increasingly effective tool in being able to predict the refractive outcome of Ortho-K treatment. Its accuracy depends on identifying which clinical and modelling metrics contribute to the most accurate prediction of RPC with minimal ocular complications. In terms of clinical metrics, age, Intra-ocular pressure (IOP), central corneal thickness (CCT), surface topography, lens decentration and the 3D eyelid effect are all important for effective modelling. In terms of FEA components, maximum principal stress was found to be the best FEA barometer that can be used to predict the performance of Ortho-K lenses. In contrast, contact pressure provided the worst stress performance. In terms of strain, the maximum principal logarithmic strain was an effective strain barometer.

The Spectrum of Ocular Manifestations among Renal Transplant Recipients

Purpose: The study aims to report various ocular manifestations among renal transplant recipients. Methods: The cross-sectional study was conducted on renal transplant patients, with at least 4 months of posttransplant duration, attending a nephrology clinic. A comprehensive ophthalmic evaluation was performed to record various ocular manifestations. The statistical association between ocular findings and pretransplant as well as posttransplant duration was assessed. Results: One hundred and twenty-three eyes of 62 patients, with a mean age of 37.6 ± 8.2 years and functional graft, were included in the study. Diabetic nephropathy was found to be the most common underlying cause of end-stage renal disease (ESRD) and renal transplant. Hypertensive retinopathy (37.4%) was found to be the most frequent ophthalmic manifestation, followed by diabetic retinopathy (24.39%), dry eye (22.76%), cataract (18.69%), and change in refractive error (17.89%). The occurrence of hypertensive retinopathy and refractive power change was found to be significantly associated with pretransplant dialysis duration. In contrast, concerning the posttransplant period, the frequency of all the major ocular manifestations, except the dry eye, was observed to be statistically significant. Conclusion: Patients with ESRD and renal transplant should be advised to undergo regular comprehensive eye examinations. Many ocular manifestations are preventable and/or treatable, thus interdisciplinary partnership between nephrologists and ophthalmologists is warranted to improve vision and quality of life in transplant recipients.

Long-Term Corneal Refractive Power Changes Two Decades After Radial Keratotomy With Microperforations.

We retrospectively examined corneal refractive power in three patients who had been followed up for more than 20 years after radial keratotomy (RK) with microperforations (MPs). All patients underwent RK in both eyes and were referred to our clinic because of postoperative decreased vision. MP was observed in five of the six eyes at the initial visit. The corneal refractive power of the anterior and posterior surfaces of the 6-mm-diameter cornea was examined using Fourier analysis based on corneal shape analysis using anterior segment optical coherence tomography. The spherical components decreased in all three cases. The asymmetry and higher-order irregularity components and fluctuations in corneal refractive power were markedly greater in the two cases with MP in both eyes. Fluctuations in corneal refractive power were observed at more than 20 years after RK with MP. Therefore, careful observation is necessary, even after a long-term postoperative follow-up period.

Changes in the total corneal refractive power after insertion of intrastromal rings in patients with keratoconus in short, medium and long term

Changes in the total corneal refractive power after insertion of intrastromal rings in patients with keratoconus in short, medium and long term

The effects of base curve aspheric orthokeratology lenses on corneal topography and peripheral refraction: A randomized prospective trial

BackgroundTo investigate the effects of orthokeratology (ortho-k) lenses with aspheric and spherical base curve designs on corneal refractive power (CRP) and peripheral refraction. MethodsChildren aged 8 to 12 years with myopia between −0.75 D to −4.00 D, astigmatism ≤1.00 D, and corneal astigmatism ≤1.50 D were randomly assigned to the base curve aspheric (BCA) and base curve spherical (BCS) ortho-k lens groups. CRP was assessed for the central 8 mm cornea along horizontal and vertical meridians, and peripheral refraction was measured at 10°, 20°, and 30° along the nasal and temporal retina. Primary measurements included relative corneal refractive power change (RCRPC) and relative peripheral refraction change (RPRC). ResultsThe 3-month results of the 33 and 29 subjects (right eye only) in the BCA and BCS groups, respectively, were obtained. Nonsignificant differences were found in the baseline data between the two groups (p > 0.05). At the 3-month follow-up visit, the mean RCRPC in the BCA group (2.08 ± 0.65 D) was significantly greater than that in the BCS group (1.32 ± 0.81 D) (F1,51 = 25.25, p < 0.001). The BCA group (-1.82 ± 0.65 D) exhibited a larger absolute RPRC than the BCS group (-0.98 ± 0.54 D) (F1,57 = 33.73, p < 0.001). ConclusionsIt was found that the BCA ortho-k lens resulted in a more aspheric treatment zone and a more myopic relative peripheral refraction (RPR) along the horizontal meridian. The more myopic RPR was contributed by a more hyperopic central refraction and a more myopic peripheral refraction in the BCA group.

Comparison of lens refractive parameters in myopic and hyperopic eyes of 6-12-year-old children.

To evaluate the influence of cycloplegia on lens refractive parameters in 6-12-year-old children with myopia and hyperopia for exploring the pathogenesis of myopia. One hundred eyes of 100 patients (50 boys) were included. In the myopic group, 50 subjects (25 boys and 25 right eyes) were enrolled with a mean age of 9.20 ± 1.69 years. IOLMaster 700 measurements were performed pre- and post-cycloplegia. The pictures were marked using semi-automatic software. The lens curvature and power were obtained using MATLAB image processing software. Paired and independent sample t-tests were used for data analysis. Statistical significance was set at P < 0.05. Anterior and posterior lens curvature radius in myopic eyes were larger than those in hyperopic eyes, both pre- and post-cycloplegia (both P < 0.001). The refractive power in myopic eyes was lower than that in hyperopic eyes without cycloplegia, both pre- and post-cycloplegia (both P < 0.001). The changes in anterior lens curvature and refractive power between pre- and post-cycloplegia in hyperopic eyes were larger than those in myopic eyes (both P < 0.05). No significant difference was found in the change in posterior lens curvature and refractive power after cycloplegia in hyperopic and myopic eyes (P > 0.05). Anterior and posterior surfaces of the lens were flatter, and the refractive power was lower in the myopia group than in the hyperopia group. Myopic and hyperopic patients showed a tendency for lens flattening and refractive power decrease after cycloplegia. Hyperopic patients had more changes in anterior lens curvature and refractive power after cycloplegia.

Measurement of the Elastic Modulus of Cornea, Sclera and Limbus: The Importance of the Corneal-Limbus-Scleral Biomechanical Unit

Energy storage, transmission and dissipation are important considerations of normal mechanical homeostasis. In this paper we present a new technique termed vibrational optical coherence tomography (VOCT) to study the anterior anatomic structures of the pig eye to better understand how energy applied to the cornea is dissipated without delamination occurring. VOCT uses infrared light and an applied sinusoidal audible sound wave to image and measure the resonant frequency and modulus of individual macromolecular components of tissue non-invasively. We have measured the resonant frequencies and calculated the moduli of tissues in the anterior portion of the pig eye using VOCT. While both pig and human eyes have similar resonant frequencies, they do differ in the peak amplitudes near the frequencies of 80, 120, 150 and 250 Hz. It is known that the stroma of pig cornea is much thicker than that of human corneas and these differences may explain the normalized peak height differences. The similarity of the resonant frequency peaks near 80, 120, 150 and 250 Hz of cornea, sclera and limbus suggest that the anatomically described layers in these tissues are connected into a single biomechanical unit that can store external mechanical energy and then transmit it for dissipation. Since the energy stored and dissipated is proportional to the modulus and the ability of the tissue to deform under stress, energy storage in these tissues is related to the stiffness. It is concluded that stored energy is transmitted to the posterior segment of the eye for dissipation through the attachment with the sclera. This mechanism of energy dissipation may protect the cornea from changes in shape, curvature, and refractive power. However, ultimately, energy dissipation through thinning of the sclera may cause globe elongation observed in subjects with myopia and glaucoma.

Investigation of the relationship between contact lens design parameters and refractive changes in Ortho-K

PurposeTo investigate the relationship between Ortho-K contact lens design parameters and refractive power change of the eye through a parametric mathematical representation. MethodsThe current study utilises fully anonymized records of 249 eyes, 132 right eyes, and 117 left eyes from subjects aged 14.1 ± 4.0 years on average (range 9–38 years) which were selected for secondary analysis processing. The data were split into 3 groups (G1 up to 35 days wear, from 10 to 35 days, G2 up to 99 days wear, more than 35–99 days & G3 more than 100 days wear) according to the length of time, in days, that the lenses were worn. Corneal shape was measured before and after contact lens wear using the Medmont E300 topographer, from which height and distance files were read by a custom-built MATLAB code to construct the corneal anterior surface independently. Changes in refractive power pre and post-Ortho-K wear were determined using constructed tangential refractive power maps from which both centrally flattened and annular steepened zones were automatically bounded, hence used to determine the refractive power change. ResultsOn average, flat Sim-K and steep Sim-K were reduced after Ortho-K lens wear by 1.6 ± 1.3 D and 1.3 ± 1.4 D respectively. The radius of the base curve was correlated with the mean central flattened zone power change strongly in G1 (R = 0.7, p < 0.001) and moderately in G2 (R = 0.4) and G3 (R = 0.4, p < 0.001). Hence, a strong correlation with the base curve was recorded in group G1 and moderate in G2 and G3. The reverse curve was very strongly correlated to the mean central flattened zone power change in G1 (R = 0.8, p < 0.001) and strongly correlated with G2 (R = 0.6, p < 0.001) and G3 (R = 0.7, p < 0.001). The reverse curve was also strongly correlated with the mean annular steepened zone power change among all groups G1, G2, and G3 (R = 0.7, R = 0.6 and R = 0.6) respectively (p < 0.001). ConclusionsAlthough the central corneal refractive power change was strongly correlated to the Ortho-K lens base curve, it characterized only 50% of the target power change. However, the annular steepened zone refractive power change appears to be a clearer predictor of target power change, as there appears to be a one-to-one inverse relationship with the target refractive power correction. Differences between these results and the literature may be a result of the topography software smoothing effect.

Establishment of Personalized Finite Element Model of Crystalline Lens Based on Sweep-Source Optical Coherence Tomography

The virtual lens model has important value in ophthalmic research, clinical diagnosis, and treatment. However, the establishment of personalized lens models and the verification of accommodation accuracy have not been paid much attention. We proposed a personalized lens model establishment and the accommodation accuracy evaluation method based on sweep-source optical coherence tomography (SS-OCT). Firstly, SS-OCT is used to obtain a single lens image in the maximum accommodation state. After refraction correction, boundary detection, and curve fitting, the central curvature radius, thickness, and lens nucleus contour of the anterior and posterior surfaces of the lens were obtained. Secondly, a personalized finite element model improved from Burd’s model was established using these individual parameters, and the adaptation process of the lens model was simulated by pulling the suspensory ligament. Finally, the shape and refractive power changes of the real human lens under different accommodation stimuli were collected and compared with the accommodation process of the finite element model. The results show that the accommodation process of the finite element model is highly consistent with that of the real lens. From the un-accommodation state to the maximum-accommodation state, the difference rate of all geometric and refractive parameters between the two is less than 5%. Thus, the personalized lens finite element model obtained by the calibration and correction of the existing model can accurately simulate the regulation process of a specific human lens. This work helps to provide a valuable theoretical basis and research ideas for the study of clinical diagnosis and treatment of related diseases.

Corneal Epithelium Thickness and Refractive Changes After Myopic Laser Corneal Refractive Surgery

To evaluate the postoperative changes in corneal epithelium thickness and refractive power after femtosecond laser-assisted laser in situ keratomileusis (LASIK) and small incision lenticule extraction (SMILE) for myopia correction using anterior segment optical coherence tomography (OCT) with an integrated Placido disc topographer. The VisuMax 500-kHz femtosecond laser (Carl Zeiss Meditec AG) and Amaris 750 excimer laser (SCHWIND eye-tech-solutions) were used. Central, paracentral, and 6-mm epithelial thickness values were obtained, and the change in the value of epithelial thickness was calculated. Changes in the refractive power of the epithelium were also evaluated. The repeatability of this new measurement was also analyzed using the intraclass correlation (ICC). The total follow-up period was 6 months. A total of 77 LASIK eyes were matched with 77 SMILE eyes. Mean spherical equivalent was -3.92 ± 1.67 diopters (D) for LASIK versus -4.02 ± 1.63 D for SMILE (P = .356). Epithelial thickness parameters significantly and equally thickened in both types of surgery. The change in the value of epithelial thickness was positively correlated with spherical aberration. Analysis of the refractive power of the corneal epithelial layer (ICC > 0.70) showed a tendency for the postoperative myopization of the refractive component of this layer (-0.11 D for SMILE and -0.53 D for LASIK at 3 mm) and an increase in its cylinder and aberrometry. Increasing postoperative spherical aberration and epithelial thickness increased myopization of the epithelial refractive sphere (P < .05). Corneal epithelium thickens similarly after LASIK and SMILE, being slightly higher after SMILE. This correlates with the induced spherical aberration. Corneal epithelium thickening induces myopization of its refractive power, which accounts for a slight regression of the net refractive power change on the treated cornea. [J Refract Surg. 2022;38(9):602-608.].

The effect of corneal power distribution on axial elongation in children using three different orthokeratology lens designs

PurposeTo investigate the correlation between spatial corneal power distribution and one-year axial length (AL) elongation using three ortho-k lens designs by a unified mathematical method. MethodsA total of 137 subjects were included: 42 with Euclid lenses, 28 with DRL lenses, and 67 with CRT lenses. AL elongation, Xmax, Ymax and power exponent were compared among the three groups. One-year relative corneal refractive power change (RCRPC) was calculated by a polynomial function and a monomial function. Factors including age, baseline spherical equivalent refractive error (SER), Xmax, Ymax and power exponent was tested against one-year AL growth in a stepwise multiple linear regression model. ResultsThe power exponent (F = 7.29, P = 0.0012) and Xmax (F = 62.88, P < 0.0001) of the DRL group was significantly smaller than that of the other two lens groups. Ymax was not significantly different among three lens groups (F = 1.18, P = 0.31). The one-year AL elongation of the DRL group (0.09 ± 0.14 mm) was significantly slower than that of the Euclid group (0.26 ± 0.14 mm, P = 0.002) and CRT group (0.32 ± 0.18 mm, P < 0.0001). AL elongation was significantly correlated with Xmax (standardized β = 0.196, P = 0.003), power exponent (standardized β = 0.644, P < 0.001), and age (standardized β = -0.263, P < 0.001), with R2 being 0.608. ConclusionA smaller and more aspheric treatment zone may be beneficial for reducing axial elongation in children undergoing ortho-k treatment, regardless of their baseline myopic refractive error.

Contribution of cornea to the peripheral ocular refraction in the two-dimensional visual field

The evaluation of the contact lenses for myopia control is often focused on the change in corneal refractive power, which is applied to indicate the contribution of the cornea to the peripheral ocular refractions (POR). However, this concept lacks a direct relationship to the POR for a realistic human eye with structural and optical irregularities. In this study, we propose a mathematically rigorous and highly efficient procedure for specifying the contribution of the cornea to the POR based on the wavefronts propagating along the chief rays from the iris center to the entrance pupil center. Using generalized ray tracing, the complexity in the impacts of the geometry of both corneal surfaces and their orientation within the human eye are fully explained with analytical equations. As a case study, the proposed procedure is performed on a realistic corneal model constructed from the measurement data on children. An approximately linear relationship has been found between the POR and the vergence of the wavefronts at the iris center for all the visual field locations. Based on this finding, we find that the contribution of the cornea to the POR can be summarized by the slope and intercept parameters derived from the linear fits in the two-dimensional visual field. The proposed analysis procedure provides a powerful tool for evaluating the peripheral optical effects of the contact lens design.

Efficacy of Low-dose Atropine Eyedrops in Myopic Progression in Elementary School Children

Purpose: We analyzed the effects of low-dose atropine on myopic progression in elementary schoolchildren aged 6-11 years.Methods: Medical records were retrospectively reviewed before and after 6 months of low-dose atropine eyedrops. Myopia was defined as a spherical equivalent &lt; -1 diopter. Low-dose atropine eyedrops (atropine sulfate 0.125% [w/v]) and artificial tear eyedrops (sodium hyaluronate 0.1% [w/v]) immediately afterwards were applied to both eyes daily, and all children regularly visited us for measurement of refractive power, axial length, pupil diameter, and near-point accommodation. symptoms (headache, light sensitivity, near-work disturbance, allergic reaction, dry eye, and poor night vision) were recorded.Results: A total of 116 patients were included. Atropine was prescribed for 65 patients, the remaining 51 patients constituted the control group. In the atropine group, the mean age was 10.2 ± 1.8 years and 23 patients (35.4%) were male. At the initial visit, the mean refractive power was -4.7 ± 2.1 diopters (D) (-1.0 to -10.5) and the mean axial length was 24.95 ± 1.02 mm (22.58-27.99). At the 6-month follow-up, the change of refractive power was -0.9 ± 1.1 D (-0.75 to -4.75) and the change of axial length was 0.47 ± 0.39 mm (0.01-1.6). However, 6 months after application of low-dose atropine eyedrops, the change of refractive power was -0.1 ± 0.2 D (0 to -0.25) and the change of mean axial length was 0.15 ± 0.23 mm (0-1.05). The mean pupil diameter was 6.7 ± 0.6 mm (5.3-9.3) and the near accommodation point was 6.1 ± 2.0 cm (3.1-11.0). Two patients (3.1%) complained of near-work disturbance but none stopped taking the eyedrops.Conclusions: Significant decreases in the changes of refractive power and axial length were evident in myopic elementary schoolchildren after low-dose atropine therapy. Low-dose atropine attenuates myopic progression without severe complications.